Abstract
A simple, mild and efficient method to prepare HSi- or HOSi-telechelic, high-molecular-weight polydimethylsiloxane polymers (to 41,600 g·mol−1) using the one-shot hydrolysis of MHMH is reported; titration of the water allowed for higher molecular weights (to 153,900 g·mol−1). The “living” character of the chain extension processes was demonstrated by adding a small portion of MHMH and B(C6F5)3 (BCF) to a first formed polymer, which led to a ~2-fold, second growth in molecular weight. The heterogeneous reaction reached completion in less than 30 min, much less in some cases, regardless of whether it was performed neat or 50 wt% in dry toluene; homogeneous reactions in toluene were much slower. The process does not involve traditional redistribution, as judged by the low quantities (<3%) of D4 produced. However, it is not possible to avoid Chojnowski metathesis from MHDDMH giving D3, which occurs competitively with chain extension.
Highlights
Polydimethylsiloxane (PDMS) oils are the parent commercial silicone polymers from which almost all other silicones are derived
Two methods dominate the commercial preparation of high-molecular-weight PDMS oil: dehydration of silanol-terminated oligomers [1] and acid- or, base-catalyzed equilibration of cyclic monomers [2] (Figure 1A,B)
Each of these approaches suffers from inherent shortcomings. The former process, as with all condensation processes, slows down with increasing conversion, which makes the synthesis of high-molecular-weight polymers challenging; both processes typically lead to polymers with high dispersities ÐM
Summary
Polydimethylsiloxane (PDMS) oils are the parent commercial silicone polymers from which almost all other silicones are derived. Two methods dominate the commercial preparation of high-molecular-weight PDMS oil: dehydration of silanol-terminated oligomers [1] and acid- or, base-catalyzed equilibration of cyclic monomers [2] (Figure 1A,B). Each of these approaches suffers from inherent shortcomings. The former process, as with all condensation processes, slows down with increasing conversion, which makes the synthesis of high-molecular-weight polymers challenging; both processes typically lead to polymers with high dispersities ÐM In the latter case, with base-catalyzed equilibration that has an equilibrium constant near 1, the desired polymer is accompanied by the formation of large quantities of cyclic monomers, e.g.,
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